<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <h2 class="counter">0</h2>
    <button class="increment">+</button>
    <button class="decrement">-</button>

    <script>
        // 获取所有的元素
        const counterEl = document.querySelector('.counter');
        const increment = document.querySelector('.increment');
        const decrement = document.querySelector('.decrement');

        // 定义变量
        let counter = 100;
        counterEl.innerHTML = counter;

        // 监听按钮的点击
        increment.addEventListener('click', () => {
            counter += 1;
            counterEl.innerHTML = counter;
        })

        decrement.addEventListener('click', () => {
            counter -= 1;
            counterEl.innerHTML = counter;
        })

    </script>
</body>
</html>